Technical Field
The present disclosure relates to skin-forming apparatus and method. More particularly, it relates to skin-forming apparatus and method that improve resin flowability and formability in injection molding of a skin and prevent product defects due to generation of gas bubbles, thereby improving external quality of a product.
Background Art
Generally, various conveniences and safety structures for a pleasant and comfortable indoor environment are mounted in a vehicle. Particularly, a crash pad is mounted in front of a driver's seat and the front passenger's seat as an indoor interior member that protects drivers and passengers when a vehicle crash occurs.
A general crash pad is manufactured using foam to exhibit elastic cushioning performance and a shock-absorbing property while exhibiting an aesthetically pleasing appearance as an interior member of a vehicle.
The crash pad may be classified into a soft crash pad and a hard crash pad. The soft crash pad includes three layers (skin, core, and foam layer), and the hard crash pad includes only one layer (core) formed by injection molding of resin.
Specifically, the soft crash pad includes a skin as a surface member for providing an aesthetically pleasing surface state, a core functioning as a frame of the crash pad, and a foam layer, such as polypropylene (PP) foam or polyurethane (PU) foam, interposed between the skin and the core for providing cushioning performance and shock-absorbing performance.
In recent years, the soft crash pad has been widely used due to advantages, such as an aesthetically pleasing appearance, better texture and cushioning, and high shock-absorbing performance.
Meanwhile, the skin of the soft crash pad, which is a portion that provides an aesthetically pleasing surface to make the interior of the vehicle pleasant and luxurious, is generally manufactured using a powder slush molding (PSM) method or a vacuum forming method.
The PSM method, which is one of the methods of manufacturing a skin of a crash pad, has advantages in design and embossing. In the PSM method, a heated mold and a material powder box are rotated to form the skin of the crash pad.
In recent years, environmentally-friendly materials, such as thermoplastic olefin (TPO) or thermoplastic urethane (TPU), have been mainly used instead of conventional polyvinyl chloride powder when using the PSM method.
The vacuum forming method is a method of manufacturing a skin of a crash pad that has been most generally used for a long time. In the vacuum forming method, a preheated TPO sheet is suctioned to a mold using a vacuum and then cooled to form the skin. A sheet having grains or a mold having grains is used to emboss the skin.
When the PSM method is used, however, a powdering process for processing material pellets, such as TPU pellets, into powder is needed, thereby increasing the cost. In addition, the mold is expensive, and excessive material scraps are generated.
For the vacuum forming method, on the other hand, when a sheet having an embossed pattern transferred thereto is formed in a vacuum, the embossed pattern may be stretched. In addition, excessive material scraps are generated.
Meanwhile, an injection molding method of injecting a raw resin, such as TPU, into a cavity of a mold through a gate using an injector and forming a skin of a crash pad may be used as another method of manufacturing a skin of a crash pad.
When a raw resin is injected into a cavity defined between an upper mold unit and a lower mold unit to form a thin-film skin, however, flowability of the resin is not satisfactory due to residual gas in the mold. In particular, gas bubbles are generated in a portion of the mold where the resin is collected.
FIGS. 1A and 1B are views exemplarily showing a skin 1 manufactured by injection molding. As shown, the skin is not properly formed or a hole is formed at a portion of the skin where gas bubbles are generated.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.